Actuators are relatively simple mechanical components that are often incorporated into more complex mechanical systems, including those found in automobiles, aircraft, manufacturing facilities, and processing facilities. A conventional solenoid is one example of an actuator that has found broad application across many types of industries and technologies.
Shape memory alloys (SMAS) are metals that exist in two distinct solid phases, referred to as Martensite and Austenite. Martensite is relatively soft and easily deformed, whereas Austenite is relatively stronger and less easily deformed. SMAs can be induced to change phase by changes in temperature and changes in mechanical stress. Also, SMAs can generate relatively large forces (when resistance is encountered during their phase transformation) and can exhibit relatively large movements as they recover from large strains. SMAs have been used commercially in many types of actuators, where a temperature change is used to initiate and control the actuation cycle. One of the most widely recognizable applications has been the use of SMA-based actuators in automatic sprinkler systems.
One disadvantage of SMA actuators triggered by changes in temperature is that a heating or cooling device must be incorporated into the actuator, increasing the size, expense, and complexity of the actuator. Further, the response of such an actuator depends on heat transfer, which can occur too slowly for certain applications. Material scientists have more recently recognized that the phase change between Martensite and Austenite can be induced by changes in an applied magnetic field in certain alloys, as well as by changes in temperature and stress loading. Because magnetic fields generated with electromagnets can be rapidly switched on and off, particularly compared to the time required to induce a change in temperature to initiate an actuation, electromagnetically controlled SMA-based actuators appear to offer promise in applications where rapidly responding actuation is required. Such alloys are referred to as FSMAs.
A particularly useful type of actuator is a membrane or diaphragm actuator. In such an actuator, deflection of a membrane or diaphragm is selectively controllable to carryout a desired function. Membrane actuators are useful in hydraulic systems and in hydraulic pumps. It would be desirable to provide improved membrane actuators.
It has been shown that active flow control technology can add external energy into a flow field that helps aircraft improve aerodynamic performance, by reducing jet noise and improving aerodynamic stall characteristics. Such active flow control can be achieved by injecting synthetic jets with high momentum air into the flow at appropriate locations on aircraft wings. For example, the Boeing Company has applied active flow control technology to rotorcraft. Currently, most synthetic jet actuators have been constructed based on piezoelectric actuator materials. However, piezoelectric materials generally do not produce forces sufficiently strong to induce strong jet flow. It would thus be desirable to provide membrane actuators capable of achieving powerful synthetic jets.
The prior art does not teach or suggest magnetically controlled SMA-based membrane actuators, or using such magnetically controlled SMA-based membrane actuators to achieve a synthetic jet.